Conducting system



May 18, 1937. TALMANN 2,080,514

CONDUCTING SYSTEM Filed Jan. 23, 1935 '1 llullll T a c F/6.4 F i i 1 a c INVENTOR 14.7?4LMANN i ATTORNEY Patented May 18, 1937 1 UNITED STATES CONDUCTING SYSTEM Asbjorn Talmami, Baltimore, Md., assignor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application January 23, 1935, Serial No. 3,125 2 Claims. (01. 173-13) This invention relates to hollow conductors and to the manufacture thereof and more particularly to the design and manufacture of coaxial conduotor cables.

For the conduction of high frequency electrical signals it is well known to employ a cable comprising a tubular outer conductor and a central return wire coaxial therewith. To provide greater flexibility than can be obtained with copper tubing and at the same time to retain the electrical advantages of the latter type of conductor, it has been proposed to construct the outer conductor of a plurality of profiled strips which are arranged to engage one another and which are held to a tubular shape by meansof an external binding member.

Such a construction is shown in a copending application for patent bearing Serial No. 630,552

filed on August 26, 1932, by J. F. Wentz, which has issued as U. S. Patent 2,018,477, October In accordance with the present invention there is provided a coaxial conductor system of the type to which reference has been made, in

which the profile of the individual strips is designed to improve the electrical and mechanical properties of the conducting system and to reduce the amount of conducting material required.

The electrical and mechanical characteristics which a tubular conductor must have to make it suitable for use in a coaxial conductor system, are not readily obtainable by the use of profiled strips! In the first place, the space between the central conductor and the tubular conductor is essentially gaseous, only so much solid material being interposed as is necessary to maintain the central conductor in position. The use of internal supporting elements for a collapsible composite structure therefore is necessarily restricted. The

thinness of the tubular conductor introduces another difliculty. Flexibility as well as economy dictates that the wall thickness be of, the order of only 20 or 30 thousandths of an inch. Diametersmay be as small as a quarter of an inch. With these dimensions it is difficult, if not impossible, to produce a rugged self-supporting conductor by the use of ordinary interlocking profiled strips. A third restriction is imposed on the length of lay of the strips. Where the strips are interlocked against relative radial movement, as in a tongue and groove construction,. added strength may be obtained by spiraling the strips.

A short spiral, although it improves the mechanical characteristics, increases the efiective resistance of the tubular conductor and introduces an undesirable circular component of current. For this reason it is almost essential in many cases that the length of lay be at least ten times the internal diameter of the conductor.

The various features and objects of the present invention will appear in the following detailed description of a specific embodiment of the invention. Reference will be made to the accompanying drawing in which:

Fig. 1 shows a composite tubular conductor and a coaxial conductor system of the type to which the present invention relates;

Fig. 2 is a cross-sectional view of the coaxial conductor structure illustrated in Fig. 1;. and- Figs. 3 and 4 show the profiles of two forms of the component strips that embody the invention.

Referring now to Fig. 1, which shows a coaxial lapping fashion and held together in tubular form by means of the binding tapes 4 and 5. A protective lead sheath 6 may be extruded over. the assemblage asshown- Any suitable means may be-employed to maintain the conductor 3 in its central position, although preferably slotted washers pressed on to the central wire at intervals of the order of three-quarters of an inch are employed for this purpose.

Fig. 2 is a cross-sectional view of the cable shown in Fig. 1. Fig. 3 shows one of the profiled strips in detail.

Heretoi'ore tubular conductors of the type shown have been made up of profiled strips, similar in several respects to those shownin Figs. 3 and 4 but in which all angles were right angles and the two portions of each strip were of equal thickness. Applicant has found that this type of tubular conductor can be improved by making the inner portion of each of the profiled strips greater in thickness than the outer portion. The. inner portions are compressional members, forced together under the tension of the binding tape. Increasing the thickness of the inner portions, so as to provide a larger bearing surface for the abutting edges, reduces the tendency for one profiled strip to slip inwardly over an ad jacent strip, particularly during the process of manufacture, and it further improves the capacity of the conductor to withstand bending and rough handling. The low frequency attenuation of the coaxial conducting system, moreover, is reduced, since at low frequencies skin effect is not great enough to confine the alternating currents to the inner surface of the conductor. It is especially important from a transmission standpoint that a smooth interior surface be obtained.

In one specific preferred embodiment in accordance with Fig. 3 where the nominal inside diameter of the conductor was 0.27 inch and nine strips were used, the dimensions in mils were as follows: a, 95.3; b, 95.3; c, 67.6; d, 65.2; e, 5.0; t, 12.4; and t 9.2.

In one embodiment in accordance with Fig. 4 where twelve strips were used, the dimensions in mils were as follows: a, 115; b, 105; c, 68; d, 68; e and f, 5.0; t, 20; t, 10.

A feature of the conductors herein described is that only the inner portion of the strips are or need be in abutting relation. The dimension n can be reduced so that a substantial gap is left between the outer portions, as indicated in Fig. 2.

In the embodiment of the invention shown in Fig. 4, both edges of the inner portion of each strip are beveled. The amount of bevel is such that when the strips are assembled as a conductor, the beveled edges are radial in direction and the strips are in contact throughout the abutting surfaces.

Various modifications of the structures herein disclosed for purposes of illustration will be obvious to those skilled in the art. The features which applicant believes to be novel with himself are set forth in the appended claims.

What is claimed is:

l. A flexible tubular conductor made up of a plurality of overlapping, interengaging strips each comprising two fiat laterally elongated striplike portions laterally oifset from each other, the inner of said portions being substantially thicker radially than the outer portions and disposed with their edges abutting the corresponding inner portions of adjacent strips, and an external member for forcing said abutting edges together, said outer portions being separated so that they do not interfere with the abutment of said inner portions.

2. A high frequency transmission system comprising a pair of coaxial conductors, connected one as the return for the other, the outer of which is a flexible tubular conductor made up of a multiplicity of profiled strips each comprising two'integral strip-like portions laterally elongated and offset from each other in difl'erent tubular layers, adjacent strips being disposed with the edges of the inner portions abutting and the edges of the outer portions spaced apart, and an external member holding said strips in assemblage, the inner portions of said strips being substantially thicker radially than the outer portions so as to provide compressionresisting strength and a relatively thick tubular shell for the transmission'of electrical waves.

ASBJORN TALMANN. 

